The invention relates to a method for checking pipes or pipe networks for leaks by filling them with liquid, placing the liquid under pressure at least in individual, separable pipe sections, and determining a change in pressure. Pipes and pipe networks are here understood to mean all types of unbranched and branched conduits of any desired cross section in which gas, liquids or dust particles are transported or which are intended for such purposes.
In a known method of this type (1) for checking the tightness of pipelines, the tightness of a pipe system is checked in that the pipe section to be checked is filled with a liquid which is put under pressure. If liquid escapes due to a leak, the excess pressure existing in the pipe will drop over time. From the drop in pressure per unit of time and from the known data regarding the pipe system and the liquid, a conclusion can then be drawn with respect to the presence and magnitude of a leak. FNT (1) "Das DD-Differenz-Druck-Verfahren zur Dichtigkeitskontrolle von im Boden verlegten Rohol-Fernleitungen", [The DD Pressure Difference Method for Monitoring the Tightness of Underground Long-Distance Petroleum Conduits], Schweizer Archiv, April 1963, pages 131-139.
The pressure test is made more difficult by the fact that changes in pressure occur even without a leak if pipe contents and pipe surroundings, e.g. soil, are not at the same temperature. The temperature equalization processes taking place between the interior of the pipe and the surroundings of the pipe cause the pressure in the conduit system or in the respective pipe section, to rise or drop. This is the case, for example, at airports where fuel is stored in tanks and is distributed to taps over an underground pipe network of several kilometers in length. Refueling processes constantly cause fuel at the tank temperature to enter the pipe system which is relatively cooler in summer and warmer in winter. Moreover, fuel quantities are stored for different lengths in the individual pipe sections, depending on the prior history of the refueling processes and consequently are able to adapt themselves more or less to the temperature of the surrounding soil. As shown in (1), a change in temperature of only 0.1.degree. K. in crude oil lines results in a change in pressure of 1 bar, independently of the volume of the pipe network. On the other hand, the same drop in pressure occurs, for example, in a pipe section containing 100 m.sup.3, whenever about 10 liters have been discharged. If a leak determination is now to be made for leaks which are less than or equal to 10 l/h, it must either be assured that the temperature in the pipe section will change by much less than 0.1.degree. K./h, or the mean temperature in the pipe section must be determined with great precision and pressure fluctuations caused thereby must be corrected by calculation. In the former case, as shown in (1), temperature equalization can be positively brought about by waiting, typically for three days, since, due to the thermostatic properties of the soil, the temperature will then remain sufficiently constant. In the second case, it is necessary in any case to have a sufficient density of measuring locations along the pipelines. Finally, a combination of both methods can also be used.
However, in the refueling system of an airport, it is untenable to have even parts only of the pipe network unused for several days. Also, installation and operation of a sufficiently tight and accurate network of temperature measuring locations would involve high expenditures.